The invention relates to a seat belt retractor, particularly to a retractor having the spool of the retractor locked by a lock bar engaging a ratchet wheel on a spool.
Some known seat belt retractors are able to lock the spool around which the seat belt is wound to prevent the spool paying out in the event of a crash. One such retractor has a spool with a toothed ratchet wheel fixed to on one end of the spool. A xe2x80x9clock barxe2x80x9d is designed to pivot between a position clear of the ratchet wheel and an engagement position in which the tip of the xe2x80x9clock barxe2x80x9d engages the teeth of the ratchet. The xe2x80x9clock barxe2x80x9d is fixed to the retractor housing and engagement of the xe2x80x9clock barxe2x80x9d with the ratchet locks the spool to the housing to prevent further pay out of the belt.
The gap between the xe2x80x9clock barxe2x80x9d and the ratchet is a critical distance that needs to be tightly controlled. It was previously necessary to use very tightly toleranced parts to reduce the possibility of dimension errors being introduced whereby the initial position of the xe2x80x9clock barxe2x80x9d is compromised. The use of such tightly toleranced parts substantially increases the cost of the retractor. Positioning the xe2x80x9clock barxe2x80x9d too close to the ratchet wheel will result in erroneous and excessively frequent engagement of the xe2x80x9clock barxe2x80x9d with the ratchet wheel. Positioning the xe2x80x9clock barxe2x80x9d too far away from the ratchet wheel will increase the time required to initiate engagement of the xe2x80x9clock barxe2x80x9d with the ratchet wheel allowing further payout of the belt prior to locking. Moreover, an xe2x80x9cearlyxe2x80x9d engagement will result in the lock bar hitting the back of the xe2x80x9cpreviousxe2x80x9d ratchet tooth. That can lead to the lock bar bouncing out of engagement with the wheel and thus not able to ensure locking of the wheel. That can also lead to jamming of the whole mechanism leading to the permanent locked state of the retractor.
A xe2x80x9clatexe2x80x9d engagement can make the lock bar hit the ratchet at a point where the dimension of the tooth is not big enough to take the load applied by the webbing on the retractor, possibly leading to breakage of the tooth.
In accordance with the invention there is provided a seat belt retractor comprising a retractor housing, a spool in the housing, a toothed ratchet wheel coupled to the spool, a locking assembly for locking the ratchet wheel to the housing comprising a lock bar moveable from an initial position to a ratchet wheel locking position whereby the lock bar engages the ratchet wheel to lock the wheel to the housing and an adjustment mechanism enabling adjustment of the initial position of the lock bar.
The components required to make the new seat belt retractor can be engineered with a larger tolerance and the initial position of the lock bar adjusted on assembly of the retractor. Because the initial position of the lock bar can be finely controlled by the adjustment mechanism the number of teeth on the ratchet wheel can be increased which further reduces the amount of seat belt pay out before and thus improves the coupling between a vehicle occupant and the seat belt system in the vehicle.
Preferably the lock bar is moved into the ratchet wheel locking position by means of the rotation of the spool.
Most preferably, the locking assembly comprises a lockcup movably mounted to the retractor housing, the lockcup including a cam surface and the lock bar includes a cam follower whereby movement of the lockcup causes the cam follower to move along the cam surface so as to move the lock bar from the initial position to the ratchet wheel locking position. The cam surface preferably comprises a slot in the lockcup.
The adjustment mechanism preferably comprises means for converting rotational displacement into translational displacement.
The adjustment mechanism is preferably received in the slot in the lockcup. In a preferred embodiment the cam follower of the lock bar comprises the adjustment mechanism.
In a preferred embodiment the adjustment mechanism comprises a body having a first part received in the slot in the lockcup acting as a cam follower a second part received in a recess in the lock bar, the first part being rotatable within the slot and the second part being rotatable within the recess, the second part being arranged substantially parallel with and offset from the rotational axis of the first part. Rotation of the first part will cause the lock bar to move so that the tip of the lock bar moves towards and away from the ratchet wheel. Rotation of the first part can effect adjustment of the lock bar into the correct initial position. Movement of the lockcup cams the lock bar into the ratchet wheel locking position.
In another embodiment the adjustment mechanism comprises a body having a first part rotatable within the slot in the lockcup and a second part comprising a toothed pinion, the lock bar including a toothed rack formed therein, the toothed pinion being received within the toothed rack whereby rotation of the first part causes rotation of the toothed pinion so as to effect positional adjustment of the lock bar.